Add NATS account-balance SoT and statement review for customers, CS, and sales

Internal billing now uses verae.billing.* request-reply and pubs. zappier-account-balance tracks prepaid, credits, usage, and payments. Portal, admin, CS, and sales all review the same statement. Independent Forgejo repos stay split via push-module-repos.

docs/sphinx/modules/zappier/credits.md

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+# `zappier/credits`
+
+**Package:** `zappier`  
+**Source:** `packages/zappier/src/credits.ts`  
+**Lines:** 30
+
+## What this module is
+
+Implementation module in `zappier`. The tables below are extracted from the source (signatures + JSDoc).
+
+## Exports
+
+`CreditAdjustment`, `CreditLedger`
+
+## Types / interfaces / classes
+
+| Kind | Name |
+|------|------|
+| interface | `CreditAdjustment` |
+| class | `CreditLedger` |
+
+## Functions
+
+_No top-level functions extracted._
+
+## Methods (class / object)
+
+| Name | Parameters |
+|------|------------|
+| `add` | `row: Omit<CreditAdjustment, 'id' | 'at'> & { id?: string; at?: string }` |
+| `list` | `customerId?: string` |
+
+## What it imports / requires
+
+_No imports detected._
+
+## Call graph (identifiers invoked)
+
+`add`, `now`, `toString`, `toISOString`, `unshift`, `list`, `filter`
+
+Each identifier is a call site in this file. Follow the import list to see the defining module; open that module’s MD for parameter and return types.
+
+## Return values (how to read this)
+
+- HTTP route handlers return Express `res.json(...)` bodies (see route docs).
+- Zapier `perform` functions return a **single object** (creates) or an **array** (triggers/searches).
+- Pricing functions return integer **cents** on `Quote.totalCents`.
+